Aseptic loosening of prosthetic implant devices is the major long-term complication after total join replacement (TIR). The local bone destruction (osteolysis) that characterizes this condition can be attributed to the induction of a granulomatous inflammatory reaction at the bone-implant interface. This tissue reaction is initiated and perpetuated by the recruitment and activation of macrophages by prosthetic wear debris. This application will focus on the physical-chemical properties regulating cell responses to particulate orthopedic implant materials, and will explore the potential role of endotoxin contamination in mediating a component of the adverse cell responses. Specific Aim 1 will test the hypothesis that particle surface chemistry and crystal structure are critical determinants of the pattern and magnitude of cell responses. Fluorescent-labeled particles of well characterized, size, shape, surface chemistry and composition will be used to define the influence of specific physical and chemical properties on protein adsorption, the kinetics of particle internalization and cytokine release. These studies will exploit the unique availability of submicron sized UHMWPE particles which exhibit properties similar to authentic retrieved PE wear debris from failed implants. Specific Aim 2 will test the hypothesis that: Lipopolysaccharide (LPS) "contamination" accounts for a component of particle-induced cell responses. These studies will define the differential capacity of particles with different surface chemistry and crystallinity of bind LPS and will assess the effects of particle-associated LPS on cell responses. Specific Aim 3 will test the hypothesis that: the molecular pathways by which particles regulate the IL-1b and TNF- genes differ and that particle-mediated effects involve LPS-dependent and -independent signal transduction systems. These experimental approaches will permit the dissection of the molecular mechanisms and signaling pathways by which foreign particulate materials modulate cell responses. The overall goal of these studies is to increase the understanding of the mechanisms by which particulate wear debris generated from orthopedic (and dental) implants regulate cell responses and to define rigorously the physical and chemical properties that determine the biological activity of the particulate materials. This information could lead to the development of targeted therapeutic interventions for preventing or modulating the adverse cellular and tissue reaction to wear particles. In addition, definition of the specific physical-chemical properties responsible for cell activation could lead to the introduction of materials that generate wear debris with reduced pro-inflammatory properties.